404CI LS2 Carburetor Engine Build - High Winder

Pumping Up A Gen IV LS2 For Serious Motor-Only Duty

Over the years we've been involved with a number of Gen III and IV engine builds and for longtime readers, you may even recognize the current LS2 that we've recently rebuilt. If so, then you'll know that this will be the third incarnation since the January '07 issue.

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Back then we had a friendly in-house competition to find out how a 402ci LS2 would fare against a conventional 406ci small-block ("Old School Meets New," page 20). All said and done, both engines generated a tick over 580 horsepower with costs being nearly identical; the biggest difference was in how docile the Gen IV was in comparison to the traditional mill. Either way, there was no clear-cut winner; instead it went to show that fairly aggressive LS engines could be built more attuned for the street at a very reasonable price.

Just under two years later, we reintroduced our mill with a completely different top end package and were able to push the power levels even higher by eclipsing the 600hp barrier with a solid-roller Comp camshaft and a set of Trick Flow 235cc cathedral port cylinder heads ("Thumper," Dec. '08, page 28). While those numbers were plenty to write home about, we went on to try the then new Zex Perimeter plate; the net results showed 780 hp and 801 lb-ft of torque!

With another year down the road, we decided to take our 402ci to the next level. Rather than topping it off with a supercharger, we wanted to see the results to be had in a naturally aspirated configuration. We'll tell you up front that this is not a street-friendly powerplant, instead it's heavily geared for the weekend dragstrip jockey with a thirst for high-test fuel.

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For the third round, we maintained a mostly similar package, only we opted for maximum compression by utilizing a set of AutoTec pistons and rings, a larger valve package by stepping up to a set of 2.10-inch on the intake side over the previous 2.08-inch valves, and made way for one of the largest Comp solid-rollers we've ever seen for an LS engine with all the supporting valvetrain, including robust springs and their shaft-mount-style rockers. For induction duties, we swapped the Edelbrock Victor Jr. manifold for a much larger Super Victor and topped it off with Quick Fuel Technology's latest three-circuit 1,050-cfm carburetor with a 4150-style base. We even borrowed a Peterson Fluid Systems oil/vacuum pump setup in order to make sure we would extrapolate every bit of power from this combination.

At the heart of our project, the credit for this creation goes to Rocco Acerrio from A.R.E. Performance & Machine in Simi Valley, California. This is a one-stop shop that offers everything from detailed machining to complete engine assembly. We're absolutely pleased with his work and if you're looking to build something similar; he's certainly the man to get the job handled.

If you thought the previous combos were something, you're gonna get a kick out of this one. For now, we're going to introduce the build, but be sure to keep an eye for the results in an upcoming issue as we put it to the test at Westech Performance in Mira Loma, California.

Quick Notes

What We Did
Put together a rowdy 404ci Gen IV

Bottom Line
Swapping a few select components can get you under way to a potent combination

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404CI LS2 Carburetor Engine Build - High Winder

Nothing out of the ordinary here, instead it's just your average factory stock Gen IV LS2 aluminum block. The original 4.00-inch bore was machined at A.R.E. Performance to 4.010-inch. By combining the 4-inch Lunati crankshaft to the new bore put us at 404 ci. For bearings, we went with a set of Clevite H-series pieces that are great for most performance applications, especially those you plan to hit the upper rpm range with.

Rocco left nothing to chance and balanced the entire rotating assembly until they met his requirements.

We ordered a set of AutoTec pistons that featured a 12cc dome and came with wristpins that weighed in at 110 grams. Should you want something a little lighter, AutoTec also offers a 105-gram wristpin option.

For rings, we went with a complete AutoTec package utilizing a 0.043-inch moly top ring, 0.043-inch cast second ring, and 3mm oil ring. Top ring endgap was set at 0.022 inch while the second ring endgap was set at 0.026 inch.

The 6.125-inch Lunati 4340 billet rods were also in great condition. We simply added a set of Clevite H-series bearings and set the clearance at 0.0025 inch. Once attached to the crankshaft, the rod bolts were torqued to 65 ft-lb with moly.

Our original Motion double-roller timing chain was in great shape, but it's always a good idea to replace them in a performance application. The cost is less than a c-note and just cheap insurance in general. For LS applications, the raised ridge is where the cam sensor takes its reading.

We reused our entire Lunati Pro Series stroker assembly. Even after years of abuse, everything looked as good as the day we got the components. We again used the ARP main stud kit and torqued the inner bolts to 60 ft-lb, 50 ft-lb for the outer bolts (both with moly), and 18 ft-lb to the cross-bolts with sealant.

While this isn't pertinent to the build, we wanted to emphasize that being organized during any build will eliminate potential headaches. Everything from the Comp solid-roller tappets to fasteners is within arms reach and easily accountable for.

In the center of the beast is this custom built Comp solid-roller camshaft. This cam isn't for the weakhearted and specs in on a 113 lobe separation and 0.834/0.800-inch intake/exhaust lift. Duration is rather stout at 0.050 with 277 degrees on the intake and 288 on the exhaust side.

Since we outfitted our TFS heads with Comp 947 springs, which feature a 1.650 diameter and 338 lbs on the seat with a 2.00-inch installed height and 850 lbs open, we needed a robust pushrod to prevent any potential deflection; our choice was Comps 3/8-inch chrome-moly Hi-Tech pushrod with a 0.080-inch wall.

To seal the cylinder heads onto the short-block, we used Fel-Pro's line of PermaTorque MLS gaskets. We've used the 1161s in the past and have had great success with them, even with big hits of nitrous. When you order them, it's important to note that they are sold individually and numbered 1161L and 1161R, for left and right. With the heads in place, Nathan Hall then torqued them to 70 ft-lb with moly.

Along with Comp's serious-duty triple springs, we added their line of titanium retainers and 1.7:1 aluminum shaft rockers. These full roller arms are just what we needed for valvetrain stability in the upper rpm range. If you're using factory valve covers, you will have to modify them slightly to fit. We're planning to reuse our Moroso sheetmetal valve covers and they cleared without any fitment issues.
Our biggest change was modifying the Trick Flow 235cc cylinder heads by swapping out the 2.08-inch valves for larger 2.10-inch valves from Si Valves. While we wanted to improve the already impressive flow figures, the 2.10 valve on the intake side also added 0.070 install height, allowing us to properly match the necessary Comp 947 triple valvesprings for the aggressive solid roller camshaft. We did the same on the exhaust side, but maintained the 1.60-inch diameter valve.

The other change was swapping over from the Edelbrock Victor Jr. manifold that's rated up to 600 horsepower for the Super Victor. This manifold stands an inch taller, has larger exit ports, and an has operating range up to 8,000 rpm.

For the oiling system, we decided to forgo the factory oil pump for an external wet sump assembly. We'll talk more about that next month, but we found that Moroso offers an affordable 7-quart oil pan with the necessary fitting, making it a very simple conversion.

To feed the fire, we're using Quick Fuel Technology's all new three-circuit 1,050-cfm carburetor. If you're looking for a carb with all the bells and whistles, then this is something you need to check out. The throttle-body is CNC machined and comes with a CNC metering block with four stages of emulsion, giving you the ability to tune for maximum performance.

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